(1) Field of the Invention
The present invention relates to an optical unit for detecting an object, and its application to a coordinate input apparatus, with a special reference made to the optical unit for detecting an object wherein a plurality of light emitting diodes are used to form a fan shape floodlight pattern, and its application for the coordinate input apparatus.
(2) Description of the Related Art
In digitizers and tablets incorporated as a coordinate input apparatus in processing units, there are various systems for detecting an angle (direction) or a position of an object. Examples are the pressure sensitive resistance membrane system, capacitance system, electromagnetic induction system and the like. There is also an optical system among non-contact systems that is capable of detecting the angle or the position of the object. In FIG. 9, a typical configuration of an optical unit used in the position detecting device of an object in accordance with conventional optical systems is shown. Light emitted from a point light source 91 is converted to a planar fan shaped light flux by a cylindrical lens 92. Then it is reflected in a 90 degree angle by a half mirror 93, and then is incident on a retroreflective member 95 which possesses retroreflective characteristics. Here, the retroreflective characteristics are the characteristics of a reflection whereby the incident light returns straight back in the direction in which the light was incident. The light incident on the retroreflective member 95 is reflected in the direction reverse to the incident direction, passes through the half mirror 93, is condensed by a lens 96 and then projected to a linear charge coupled device (CCD) 97. In the case of a position detecting device using a light interruption system wherein a retroreflective member is provided at an edge of the effective region, and a shadow is used, as the object interrupts the light, in order to detect the direction of the object, the direction of the shadow can be detected from the distribution of the output signals of the linear CCD 97. However, since this example uses the half mirror 93, the attenuation or loss of the light at the time of reflection at and at the time of passing through the half mirror 93 cannot be avoided. Also, as illustrated in FIG. 10, there is a system, which uses a reflecting mirror 94 with a slit in lieu of the half mirror in the conventional optical unit shown in FIG. 9. A problem in this case is that only a portion of the light reflected by the retroreflective member can be used as input light to the linear CCD.
As another example of an object detecting device, which detects the angle or the position of the object optically, there is one disclosed in Japanese Patent Application Laid-Open No. S62-5428. This device is configured such that the two optical units respectively project light in a fan shape, parallel to a coordinate detecting surface, and the linear photoreceptive sensor receive the retroreflective light from a retroreflective surface provided at an edge portion of the coordinate detecting surface, the edge portion being opposite to the location where the two optical units are provided. By interrupting a portion of the light with an object, a finger or a pen, the device detects the direction of the shadow. By conducting this detection from the two optical units which are arranged in the predetermined positions, the coordinates of the finger or the pen can be calculated accurately with the triangulation principle explained later.
Almost the same prior art system is disclosed in the U.S. Pat. No. 4,507,557. This example configures the system with a stand-alone light emitting diode with broad directivity and high-power, in which the light emitting diode is used as a stand-alone light source without inolving a lens or a mirror.
In Japanese Patent Application Laid-Open No. H9-319501, a system which uses a position sensing device (PSD) as a photoreceptive sensor instead of a linear CCD is disclosed. PSD is a component which generates different electric signals by light-receptive spots, having one-to-one correspondence between the light-receptive spot on the PSD and the light-receptive angle of the reflective light from the pen. This light is, then, incident on the angle detective means, so that by predetermining the correspondent relationships among the light-receptive angle, the light-receptive spot on the PSD and the electric signal that the PSD generates, then from the value of the electric signal directly measured by the PSD, the pointing position of the pen can be identified. In this prior art, an LED and a cylindrical lens are arranged in such a way as to cause the emitted light from the LED to become a beam parallel to the coordinate input surface by the cylindrical lens which is placed right in front of the LED. In these types of optical object detecting devices, the field of the photoreceptive sector becomes a fan shape plane, especially, in the case of the detecting device wherein an array of a linear photoreceptor is provided at the photoreceptive sector so that the light from the object or the direction of the shadow of the object is detected. Then, in the case of providing the retroreflective member on the object and using the retroreflective light from the object itself, or in the case of providing the retroreflective member at the opposite edge of the effective region, and using the shadow in the case of the object interrupting the light, the retroreflective light, then, returns back through the same path as the projected light, so that it is necessary that the light source which projects the light in a fan shaped projection pattern and the light-receptive sector to receive the retroreflective light be provided as closely as possible. In recent years, material which has excellent retroreflective characteristics has become available, so that the efficiency of light can be improved greatly by placing the projection pattern and the light-receptive pattern close together. Then, it is possible to arrange that the light projection sector and the light-receptive sector be completely coincided by using the half mirror or the reflective mirror with a slit as in the cases of FIG. 9 or FIG. 10 respectively. However, in these cases there is a problem of aforementioned attenuation of the light, or only a portion of the light is effectively received.
In general, a point light source and a cylindrical lens can be used to form a fan shaped projection pattern. For the light component at a surface perpendicular to the projected surface of the fan shaped projection pattern, parallel rays are ideal.
As an example of optical means to realize a so-called electronic blackboard, which has a large input surface, there is Japanese Patent Application Laid-Open No. H11-85377. In this example, a laser beam is used as the light source, and a polygon mirror conducts scanning on the blackboard. A defect in this kind of device is that there is a difficulty to determine the position of the optical unit and to adjust its angle. To solve such a problem of having difficulty to adjust the attachment angle of an optical unit in such devices, Japanese Patent Application Laid-Open No. H11-85399 suggests fine adjustment of the height and inclination of the optical unit with a screw.
The U.S. Pat. No. 4,107,522 can be cited as an example of using a stand-alone optical unit for detecting the object. This is to realize a security system, in which one light emitting diode is used for the projection sector.
In recent years, a so called input/output consolidation type coordinate input device has been realized. Here, the input surface of the coordinate input device and the display surface, such as, the liquid crystal display device are caused to be placed one over the other. Among the input/output consolidation type coordinate input devices, an electromagnetic induction system has been used for the one which can input handwriting letters by using a pen. In this case, antennas for detection of electromagnetic flux are provided in the back of the liquid crystal display. For the one that can be operated by a finger, it has transparent touch panel deployed before the display device. The touch panel uses a matrix electrode system with a transparent conductive sheet, or uses a system to detect the interruption of a plurality of light beams aligned vertically and horizontally.
In the optical units illustrated in FIG. 9 or FIG. 10, or the system to specify the position of the object by using light as proposed in Japanese Patent Application Laid-Open No. S62-5428, a reflective mirror is used to irradiate light. This reflective mirror cannot project an appropriate amount of light onto the surface of the detecting region without conducting a precise adjustment. As the detecting region gets larger, a slight deviance in the attachment angle of the reflective mirror at one edge is amplified as a large deviance at the other edge of the detecting region, thereby making the adjustment extremely difficult. Further, in the case of using a point light source and a lens as a means for projection, a fine adjustment of respective positions is required. With the reflective mirror added to the scene, they influence each other, causing complex adjustment to be required for the actual assembly task.
This reflective mirror, in order to guide the reflected light to the photoreceptor, requires the provision of a space such as a slit or the like, or requires the reflective mirror itself to be composed of the half mirror, so this system has a problem of producing a loss of the light. For example, in the case that the reflective mirror is composed of a half mirror, and the light from the point light source reflected at a 90 degree angle by the half mirror is reduced to half of the light quantity, and the light received by the linear photoreceptor after the reflected light from the retroreflective member passes through the half mirror is reduced to half again, producing altogether, xc2xe of the light loss.
Also, to get enough quantity of light with only one LED, as is disclosed in the U.S. Pat. No. 4,507,557 and the U.S. Pat. No. 4,107,522, a high power and expensive light emitting diode is required, and a special diode with broad directivity is required. Further, in the case of Japanese Patent Application Laid-Open No. H9-319501, a point light source of LED and a cylindrical lens are used for the light source, which require a very delicate adjustment.
Further, in the case of Japanese Patent Application Laid-Open No. H11-85377, wherein a laser beam is used, an expensive laser diode is required, and a special attention must be paid in the handling of the laser beam. Further, in this system, as a polygon mirror is rotated to scan the laser beams, a physical mechanism for rotation and a motor to rotate it are necessary, thereby causing it difficult to make the optical unit itself compact.
The present invention provides an optical unit for detecting object, which does not use a reflective mirror or a lens as used in the prior art, and does not require a delicate adjustment of the position, and is realized at a low price, and it also provides a coordinate input apparatus using such optical unit.
According to the present invention, there is provided an object detecting optical unit for detecting a direction or a position of an object, which is placed on a detecting plane surface and irradiated by light, by detecting existence or non existence of a retroreflective light reflected by a retroreflective member, the optical unit comprising:
a light projection means having a plurality of light sources and a plurality of lenses which correspond to the light sources, wherein the plurality of light sources and the plurality of lenses are arranged in such a manner as to form a fan shaped projection pattern parallel to the detecting plane surface, the projection pattern being as if projected from a virtual one point light source; and
a light receiving means having a slit, or a lens and linear photoreceptive group, wherein the slit or lens and the linear photoreceptive group are arranged in such a manner as to form a light receiving pattern with a view field corresponding to the fan shaped projection pattern formed by the light projection means.
By configuring a plurality of point light sources and a plurality of lenses to form a virtual one point light source, a stronger point light source is realized. The point light source used here is meant for the point light source in the case of the fan shaped light seen in a two-dimensional plane, and not for the point light source seen in three-dimensional space.
The projection means is formed by a plurality of light emitting diodes. A light emitting element in each light emitting diode forms one of the plurality of light sources. A transparent package of each light emitting diode forms one of the plurality of lenses.
The light emitting diode is usually enclosed in a clear resin package, which has a lens function. Such light emitting diodes are arranged in a fan shape to attain a projection pattern close to the ideal pattern.
Further, the plurality of light sources and lenses may well be arranged in such a way that each center of their optical axis, projected from each light source through a lens, corresponds to the optical axis of the projected pattern, wherein an assembled location at one point in the back of the light sources is made to be the virtual point light source and as if a fan shaped projection pattern is projected from thereat. It is also possible to make an arrangement by substituting the assembled location at one point in the back of the plurality of lenses with an assembled location at one point in front of the lenses, the one point being the virtual point light source to form a fan shaped projected pattern from there.
The projection means can be provided to either the topside or the bottom-side of the detecting means with a slight deviation to the perpendicular direction in relation to the aforementioned detecting plane. Further, the projection means may well be provided to both the top and bottom sides to increase the projection amount as a whole.
Further, the coordinate input apparatus in accordance with the present invention is constituted by at least the two optical units for detecting the object, each of the optical units being provided to its predetermined position, direction of the object being calculated by each of the optical units, thereby calculating the coordinates of the object by the triangulation principle, and inputting the coordinate information into an information processing apparatus. In this way, the accurate detection of the coordinates of the object becomes possible.
Further, the coordinate input apparatus in accordance with the present invention comprises a display device for displaying the information outputted from the information processing apparatus, the display device being provided right underneath the detecting plane. By configuring the light source of the optical unit in such a way that the plurality of point light sources are as if they are one point light source, it has become possible to realize an input/output consolidation type coordinate input apparatus combined with a large size display device at low cost, whereas conventional optical units for such a large size consolidation type device have been very expensive.